Who Is Star-Lord’s Father?

At the very end of Guardians of the Galaxy Nova Prime tells Peter Quill that they've discovered something about his physiology: he's only half-Terran. His mom, who we saw on her death bed at the beginning of the film, was from Earth but his dad was something non-terrestrial, and something more ancient than the Nova Corps had ever seen. This comes on the heels of the revelation that Quill had been kidnapped by the Ravagers to deliver the boy to his father, who Yondu calls a jackass. That leaves a small mystery for Guardians 2: who is Quill's dad?